Alex, In your original post I thought you were looking for RF grounding. This sounds like you are talking about a signal via. If so: 1. You need a path for the return current close to the signal via. If you have room, you can place ground vias around the signal via to form a vertical transmission line in the board. Controlling this impedance gets more critical as the board gets thicker and the frequency goes up. 2. The size and distribution of pads and anti-pads can be designed. 3. In general, transitions from microstrip into the via tend to be inductive. Leave the pad in the groundplane layer in place and minimize the anti-pad dia. You actually want extra capacitance to compensate the inductance. 4. In general, stripline transitions tend to have excess capacitance. So you remove the pad or pads in the adjacent ground plane layers and increase the anti-pad diameter. 5. I do this on a field-solver by optimizing for return loss across the frequency range of interest. I have used this general approach for transitions up to 10 GHz and up to 16 layers. Dan Dan Swanson EMAIL: d.swanson@xxxxxxxx Bartley RF Systems, Inc. TEL: 978-834-4085 37 South Hunt Road FAX: 978-388-7077 Amesbury, MA 01913 On Monday, September 24, 2001 6:23 PM, Alex Horvath [SMTP:alexh@xxxxxxxxxxxxxxxx] wrote: > I found a source that describes an RF via (which is bad terminology, I know) > as follows: > > 1. Large anti-vias (do they really mean anti-pads). > 2. No pads on power and ground planes. > 3. No pads on signal planes that are not used. > > > > -----Original Message----- > From: si-list-bounce@xxxxxxxxxxxxx > [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Perry Qu > Sent: Thursday, September 20, 2001 9:54 AM > To: DSWANSON@xxxxxxxxxxxxx > Cc: 'alexh@xxxxxxxxxxxxxxxx'; Si-List > Subject: [SI-LIST] Re: RF via > Importance: High > > > > Hi! > > I would imagine that RF via is similiar to a coax structure, where you have > several return vias surrouding the signal vias. This is to match 50 ohm > impedance as close as possible and reduce the discontinuity effect of the > vias. > > Regards > > Perry > > Dan Swanson wrote: > > > Physically short, close to the component. > > Lowest impedance path possible to true ground, > > not the local ground. Via always has some > > finite inductance. > > > > Dan > > > > On Wednesday, September 19, 2001 5:14 PM, Alex Horvath > > [SMTP:alexh@xxxxxxxxxxxxxxxx] wrote: > > > > > > What are the particulars of a "rf via"? > > > > > > I'm using a component which switches at 2 Ghz that recommends the use of > > > this type of via. > > > > > > > > > ------------------------------------------------------------------ > > > To unsubscribe from si-list: > > > si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field > > > > > > or to administer your membership from a web page, go to: > > > //www.freelists.org/webpage/si-list > > > > > > For help: > > > si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field > > > > > > List archives are viewable at: > > > //www.freelists.org/archives/si-list > > > or at our remote archives: > > > http://groups.yahoo.com/group/si-list/messages > > > Old (prior to June 6, 2001) list archives are viewable at: > > > http://www.qsl.net/wb6tpu > > > > > ------------------------------------------------------------------ > > To unsubscribe from si-list: > > si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field > > > > or to administer your membership from a web page, go to: > > //www.freelists.org/webpage/si-list > > > > For help: > > si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field > > > > List archives are viewable at: > > //www.freelists.org/archives/si-list > > or at our remote archives: > > http://groups.yahoo.com/group/si-list/messages > > Old (prior to June 6, 2001) list archives are viewable at: > > http://www.qsl.net/wb6tpu > > > > -- > Perry Qu > > Product Integrity | 600 March Road > Alcatel Canada | Ottawa, ON K2K 2E6, Canada > > DID: (613) 7846720 | FAX: (613) 5993642 > > > ------------------------------------------------------------------ > To unsubscribe from si-list: > si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field > > or to administer your membership from a web page, go to: > //www.freelists.org/webpage/si-list > > For help: > si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field > > List archives are viewable at: > //www.freelists.org/archives/si-list > or at our remote archives: > http://groups.yahoo.com/group/si-list/messages > Old (prior to June 6, 2001) list archives are viewable at: > http://www.qsl.net/wb6tpu > ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu